1. Field of the Invention
The present invention relates to a low melting point glass suitable for covering for insulation of transparent electrodes made of e.g. ITO (indium oxide doped with tin) or tin oxide, particularly transparent electrodes having a silver electrode formed on a part of their surface, a colored powder and a plasma display device.
2. Discussion of Background
In recent years, a thin flat plate type color display device has attracted an attention. In such a display device, it is necessary to form an electrode for each pixel in order to control the display state in the pixel for forming an image. In order to prevent deterioration of the image quality, transparent electrodes are used as such electrodes. As the transparent electrodes, thin films of ITO or tin oxide formed on a glass substrate, are commonly employed.
Transparent electrodes which are formed on the surface of a glass substrate to be used as a display panel of the above display device, are formed into fine lines to realize fine images. In order to control the respective pixels independently, it is necessary to secure insulation among such finely formed transparent electrodes. However, if moisture is present on the surface of the glass substrate, or if an alkali component is present in the glass substrate, it may happen that an electrical current flows to some extent via the surface of this glass substrate. To prevent such a current, it is effective to form an insulating layer between the transparent electrodes. Further, in order to prevent deterioration of the image quality by the insulating layer formed between the transparent electrodes, such an insulating layer is preferably transparent.
Various materials are known as an insulating material for forming such an insulating layer. Among them, a glass material is widely employed which is a transparent and highly reliable insulating material.
In a plasma display panel (hereinafter referred to as PDP) which is recently expected as a large size flat color display device, cells are defined and formed by a front substrate used as a display surface, a rear substrate and barrier ribs, and an image will be formed by generating plasma discharge in the cells. Transparent electrodes are formed on the surface of the front substrate, and it is essential to cover the transparent electrodes with a glass in order to protect the transparent electrodes from plasma.
Such a glass to be used for covering electrodes, is employed usually in the form of a glass powder. Namely, to such a glass powder, a filler, etc. may be added as the case requires, and then the mixture is formed into a paste. The glass paste thus obtained is coated on a glass substrate having transparent electrodes preliminarily formed, followed by firing to cover the transparent electrodes.
In addition to the electrical insulating property as mentioned above, the glass for covering electrodes is required to have e.g. a softening point of at most 650° C., a linear expansion coefficient of from 60×10−7 to 100×10−7/° C. and a high transparency of the electrode-covering glass layer obtained by firing.
As a glass satisfying such requirements, a glass comprising 45% of PbO, 41% of B2O3, 3% of SiO2 and 11% of MgO, as represented by mass percentage, is, for example, disclosed (JP-A-2000-313637).
The relative dielectric constant at 1 MHz of the disclosed glass is as small as 9.6, and the dielectric constant of the electrode-covering glass layer is small, whereby it is excellent in that the electric power consumption of PDP can be reduced.
However, with PDP, there may be a case where it is required to increase the dielectric constant of the electrode-covering glass layer in view of e.g. a problem relating to an electrical circuit.